Method of making electrodes



Aug. 22, 1950 D. F. DRIESCHMAN METHOD OF MAKING ELECTRODES 2Sheeis-Sheet 1 Original Filed Aug. 31, 1943 V mm M m k E v 0' V .x m M UM. m

Aug. 22, 1950 D. F. DRIESCHMAN 2,519,445

METHOD OF MAKING ELECTRODES Original Filed Aug. 31, 1945 2 Speeps-Sheet2 INVENTOR. Dona/d ff Dn'escfiman HA5: ATTORNEY Patented Aug. 22, 1950*U NIT ED S TATES JPAT ENT ()FFFFKZEI METHOD OF HEARING ELECTRODESDonald F. Driescliman, Los Altos, Calif, ass'ignor to Eitel-Mo'Cullough,Inc, San Bruno,0alif., a corporation of Oalifornia Original applicationAugust 311, I943, -Seria-lNo.

1947, Serial 'No. 750,239

'1- Claim. 1

This is a divisionof parent application Serial No. 500,717, nowabandoned, which parent application discloses an improved welded jointadapted for use in the fabrication of electrodes such as cathodes forvacuum tubes. Theclaims in the parent application are directed 'tothewelded joint, and the claim of thisdivisional'application are directedto the method of making an electrode. Another divisional applicationSerial No. 552,310, new Patent No. "2,442,163, granted May 25, 1948,contains claims'directed to the electrode structure.

It is among the objects of my invention to provide an improved method ofassembling and welding an electrode such as a cathode. 7

The invention possesses other objects and features of advantage, some ofwhich, with the foregoing, will be set forth in the followingdescription of my invention. It is to be understood that I do not limitmyself "to this disclosure of species of 'myinvention a'sl may adoptvariant embodiments thereof wi'thin'the scope of the claim.

Referring to the drawings:

Figure l is a side elevational view of a cathode structure made "byyxim-proved method; and

Figure '2 is an enlarged detail sectional View taken in plane indicatedby line 2-2 of Figure 1.

Figure 3 is an exploded vertical sectional View of the cathode andassembly jig.

Figure 4 is a vertical sectional view of a cathode in a-bell jar readyfor arc welding.

Figure 5 is a plan view of a modified arrangement for welding, using ahigh frequency coil.

In terms of broad inclusion, my method of making an electrode comprisesarranging a metallic element, such as a filament wire, with an endadjoining a metal support, coating the jo nt with a paste containingparticles of metallic welding material, and then subjecting the joint tosu'fiicient heat to melt the particles to weld the element to thesupport. In the'case of a cathode structure the filament wires arepreferably arranged about -a cylindrical bore,

which core is removed after the coating and heating steps. In order todivide one end of the cathode into sections, and to facilitate removalof the core, I prefer to sever the support between certain of thefilament wires after the welding operation.

In greater detail, and referring to the drawings, my improvements areillustrated in conjunction with an electrode for a vacuum tube, and moreparticularly to a cathode structure.

Divided and this application May 24,

As shown in Figures 1 and 2, the cathode comprises a multiplicity of say40 parallel wires 2 of thori'ated tungsten divided into four groupsdisposed in cylindrical formation about the cathode axis, "each group ofwires being connected at the lower'end to one 'ofthe fourtungs'tencathode leads 3 and allbeing connected .at the upper "end to acommon'terminal i.

Fixed supports "for the lower ends of theiilament wires are provided bybrackets B welded to the leads and to quadrant sections 1 havingarcuat'e rims to which the groups of filament wires are welded. Leads '3are sealed in afourway press c on asuitable-stem '9 "of g lass or thelike. The upper support or terminal '4 is a cap having a circular 'rimto which the upper ends of the filament wires are welded. These upperand lower supports .are of a refractory metal such as tantalum ormolybdenum, tantalum being preferred.

Top cap 4 .provides a movable support and is held centered by atungsten-rod-orstandard II sealed to the stem and projecting through thecap. Tension is uniformly applied to all the filament wires by a sleevel2 slidable along the center rod and urged upwardly against cap 4 by aspring '53 interposed between the sleeveand 'ste'm.

In the'final tube diametricallyopposed cathode leads aare connected .inzparallel toasource of heating current. Since two of the groups-offilament wires are connected in series with one pair of leads and theother two groups are connecied in series with the other two leads, allof the filament wires are simultaneously heated.

This structure has the advantage of compacting a multiplicity offilament wires in a relatively small circle, whereby a large amount ofelectron emitting surface is made available.

The main problem in fabricatingsuch astrucis, of course, securing theends of the filament wires to the supporting members. Ordinary spotwelding-practice is not feasible because of'the close spacing betweenthe wires. I have solved the problem by a special welding material andwelding technique, resulting in the formation of a bonding medium orlayer M in which the filaments are embedded. See Figure 2. This layerpreferably comprises an alloy composed of a major proportion ofcolumbium and a minor proportion of ruthenium, the preferred proportionsbeing about 4% to 20% by weight of ruthenium and the balance columbium.Other refractory metals such as tantalum may be substituted in whole orin part for the columbium component of the alloy. Likewise other metalsin group 8 of the periodic table may be substituted for the rutheniumcomponent. However, the columbium-ruthenium composition is superior inmany respects and is preferred. This alloy has a high melting point, lowvapor pressure, is very hard and makes an excellent bond betweenrefractory metals such as tungsten and the like. These properties makethe alloy especially suited for a joint structure in a cathode l whereexceedingly high temperatures are involved.

The preferred method of making the cathode utilizes a jig (Figure 3)comprising a cylindrical core l6 of say copper having longitudinalgrooves in the surface to receive filament wires 2, the latter beingstraight, rod-like pieces cut to size. These wires are temporarily heldby a rubber band I1; core I6 being proportioned so that wires 2 projectfreely from the ends. At this stage of fabrication the quadrant sectionson brackets 6 are formed as a one-piece ring 13 which is later severedat four places to make the individual quadrants. Ring I8 is inserted atthe lower end of the jig-held filament wires and top cap 4 is insertedat the upper end, the jig core being sized to hold wires 2 in a circleslightly smaller in diameter than that of the end supports so that thelatter are held by press fit during the welding operation. As shown inFigure 4, a handle I9 is threaded into core I6 to permit moving theassembled cathode up into a bell jar 20 for welding purposes.

The welding material used to produce the preferred bonding allow at theweld comprises a mixture of finely divided particles of columbium andruthenium. The columbium particles should not be larger than about 200mesh, a particle size of around 400 mesh being preferred. The rutheniumparticles used are preferably still more finely divided, a powder knowncommercially as ruthenium black being preferred. These particles aremixed together with a liquid vehicle, such as water, to a thin pastyconsistency suitable for application with a brush. This welding materialis then brushed onto the rims of the supports and over the end portionsof the filament wires as shown at l in Figure 4.

With the welding material applied the assembled cathode is then elevatedin hell jar to position the upper support near an electric arcdischarging between electrodes 2| sealed to the sides of the bell jar.Rotation of the cathode by the operator exposes successive portions ofthe rim to the intense heat of the arc. After finishing the top weld thestructure is moved up to weld the filaments at the lower support. Anonoxidizing atmosphere is maintained in the bell jar by admitting agas, such as hydrogen, through a suitable duct 22.

In making these welds I find that the welding material melts and flowsout uniformly and smoothl over the joint. The ruthenium performs animportant function at this stage, serving as a wetting agent and to giveuniform spreading of the material over the surfaces. The finalcomposition formed by the columbium and ruthenium is a hard, tough alloyhaving good bonding affinity for other refractory metals such as thetungsten filaments 2 and tantalum supports 4 and I8. These propertiesinsure strong mechanical joints at the ends of the filaments.Furthermore, the high melting point and low vapor pressure of thebonding medium produces a weld which will readil withstand theincandescent operating temperatures of the filament wires.

Instead of using an arc the heat required for making the weld may besupplied by high frequency induction, using a coil 23 as shown in Figure5; this coil being positioned in a suitable bell jar so that thenon-oxidizing atmosphere may be supplied. The assembled cathode on thejig is elevated to place the desired portions of the cathode within thecoil, whereupon the coil is energized to induce the required amount ofheat. Since lower support I8 is a continuous ring at this time theinduction heating method may be used at the bottom as well as at the topWelds.

After the welds are completed ring [8 of the lower support is cut infour places between brackets 6 to separate it into the quadrant sections 1 Shown in Figure 1. Jig core 16 is then removed by spreading thelower end of the cathode. The cathode is now ready for final mounting,together with the spring tensioning device, on stem 9.

While I have described my improvements par ticularly in connection witha cathode it is understood that the method may be used in connectionwith other electrodes such as grids in which wires are welded to endsupports.

I claim:

The method of making a cathode structure which comprises assemblingparallel filament wires on and lengthwise of a cylindrical core withends of the wires adjoining the rim of a metal support to form therewitha joint, coating the joint with a paste containing particles of ametallic welding material, subjecting the joint to suflicient heat tomelt the particles to weld the wires to the support, severing thesupport between certain of said filament wires and then removing thecore.

DONALD F. DRIESCHMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 401,444 Lemp et a1. s Apr. 16,1889 2,232,176 Guthrie Feb, 18, 1941 2,339,402 Herzog Jan. 18, 19442,391,969 Herzog Jan. 1, 1946 2,400,082 Eitel et a1. May 14, 19462,402,029 Dinnick et al June 11, 1946 2,433,339 Brown Dec. 30, 1947

